Friday, July 4, 2014

Butterfly milkweed having an especially great year

Black Earth Rettenmund Prairie State Natural Area is always one of the great sites for the showy butterfly milkweed (Asclepias tuberosa), but this year is especially nice. I counted 180 plants, mostly fairly large, in a small (1 acre) patch which is representative of most of the 16-acre prairie remnant. The photo here, of the South Unit, is typical. The area we call the "Saddle" is also especially nice, but the whole prairie is in full bloom.

This species does especially well in dry mesic prairies such as Rettenmund, where it is found in association with lead plant, Coreopsis palmata, prairie rose, compass plant, rosin weed, big bluestem, needle grass, prairie dropseed, and rough blazing star.

The following observation indicates that butterfly milkweed self-seeds well. Adjacent to Rettenmund Prairie is a 3 acre pasture that has not been grazed in about 20 years. When grazing was discontinued there were no prairie plants at all.

We have been burning this pasture biennially since 2002. Nothing has been done to this pasture except burning, yet as the years have gone by it has turned into a prairie remnant dominated by little bluestem, with a few scattered forbs. About four years ago, butterfly milkweed plants started to appear, and the number has gradually increased. This year the number of milkweed plants is quite large, as the photo below shows.

Former pasture now rich in milkweeds. Subjected only to biennial burns.

This is a dramatic example of the ecological power of fire!

An interesting fact about butterfly milkweed is that in contrast to all the other milkweeds it does not have a milky sap.